Carbon Crystallization during High-Temperature Pyrolysis of Coals and the Enhancement by Calcium
Carbon Crystallization during High-Temperature Pyrolysis of Coals and the Enhancement by Calcium
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DOI：
10.1021/ef020265u
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发表时间：
2003-07
期刊：
影响因子：
5.3
通讯作者：
N. Tsubouchi;C. Xu;Y. Ohtsuka
中科院分区：
文献类型：
--
作者：
N. Tsubouchi;C. Xu;Y. Ohtsuka
使用固定床和自由落体反应器在 1000−1350 °C 和不同的加热速率下对五种煤进行热解，以检查脱挥发分焦中的碳结构。 X 射线衍射测量显示具有乱层结构的结晶碳的形成，很大程度上取决于煤的类型和热解的严重程度。低阶煤的碳比例通过酸洗脱矿而降低，但通过随后添加 Ca2+ 离子而相反增加，无论加热速率如何，少量 0.5−1 wt% Ca 即可有效发挥作用。因此，低阶煤中以离子交换形式自然存在的 Ca2+ 离子很可能主要决定了较高温度下碳结晶的程度。添加的Ca在热解时转变成细颗粒的CaO，并且在Ca的存在下形成大量的CO。从 CaO 颗粒之间的固-固相互作用的角度讨论了 Ca 增强碳结晶的机制。
Pyrolysis of five coals has been carried out at 1000−1350 °C and different heating rates with fixed-bed and free-fall reactors to examine carbon structures in devolatilized chars. The X-ray diffraction measurements show the formation of crystallized carbon with turbostratic structures, depending strongly on coal type and severity of pyrolysis. The proportion of the carbon with low rank coals decreases by demineralization with acid washing but contrarily increases by subsequent addition of Ca2+ ions, irrespective of heating rate, and a small amount of 0.5−1 wt % Ca works efficiently. It is thus likely that Ca2+ ions naturally present as ion-exchanged forms in low rank coals determine dominantly the extent of carbon crystallization at higher temperatures. The Ca added is transformed to fine particles of CaO upon pyrolysis, and a larger amount of CO is formed in the presence of the Ca. A mechanism for the Ca-enhanced carbon crystallization is discussed in terms of solid−solid interactions between CaO particl...